We are investigating the role of lactoferrin, a major milk protein, and the serum iron binding protein transferrin in the mixed lymphocyte reaction (MLR). We have found that both these proteins are stimulatory in the MLR> Also the antibacterial activity of these molecules is being explored. A paper by Labib and Tomasi in press reports that bovine secretory component (SC) and gamma-glutamyl transpeptidase are two distinct proteins. Characterization of this enzyme is under investigation. Further sequence studies on the bovine SC to determine if any significant homologies occur between SC and immunoglobulins are underway.